The present invention relates to a fuel hose of a two layer structure, which is excellent in interlaminar adhesion and has an antistatic function.
Heretofore, a fluororesin is used in a wide range of fields, since it is excellent in e.g. heat resistance, chemical resistance, weather resistance, non-tackiness, low frictional nature and low dielectric property. For example, use as a surface covering material to cover a substrate is known wherein a film or the like of a fluororesin is laminated on the surface of a substrate made of an inorganic material such as a metal or glass or an organic material such as a synthetic resin. Further, as an important application to a laminate, a fuel hose may be mentioned which is used in an engine room of an automobile and which is exposed to a severe condition such as a high temperature environment.
The fuel hose is a hose for piping, wherein a gasoline fuel containing an alcohol or an aromatic compound is transported. In recent years, regulations relating to permeation of gasoline have become severer, and as a measure to cope with such requirements, a hose of a multilayer structure such as a two layer structure, has been proposed, and especially for the inner layer which is directly in contact with the fuel, it is desired to use a resin having chemical resistance against a corrosive material such as ethanol or methanol present in the fuel and a gas barrier property not to let such a material permeate. From such a viewpoint, a fluororesin having heat resistance, chemical resistance and gas barrier property, is considered to be one of the most preferred materials, as the material for the inner layer.
However, the fluororesin forming the inner layer has a high insulation property, whereby static electricity is likely to form and electrification is likely to result when a fuel passes in the hose. Accordingly, leakage of the fuel due to formation of a hole in the hose, and various problems due to electric discharge, are likely to result. Therefore, it is necessary to prevent electrification of the fluororesin, for example, by imparting electrical conductivity to release the formed static electricity.
On the other hand, for the outer layer of a fuel hose, it is common to use a polyamide resin such as polyamide 6, polyamide 11 or polyamide 12, which has relatively good durability.
Heretofore, there has been the following problem when it is attempted to construct a fuel hose having a two layer structure comprising an inner layer made of a fluororesin and an outer layer adjacent thereto, made of e.g. a polyamide. Namely, the fluororesin is, by its nature, a material having a low adhesive property, and even if it is attempted to fuse a tube of a fluororesin directly to the base material of the outer layer, no adequate bond strength is obtainable. Further, even if a bond strength of a certain degree may be obtained, the bond strength is likely to vary depending upon the type of the base material, whereby there has been a problem that the bond strength is practically inadequate.
Under these circumstances, an attempt has been made to make a hose of a three layer structure wherein a layer of an adhesive is interposed between an inner layer of a fluororesin and an outer layer of a polyamide resin.
However, as compared with a fluororesin, such an adhesive is inadequate in chemical resistance, water resistance and heat resistance, and not infrequently, such a portion has been a cause of a problem in the laminated structure employing a fluororesin. Further, from the viewpoint of the production process, in order to use an adhesive, a step of surface treatment of the fluororesin or a step for primer treatment has been required in many cases. Further, a step of laminating an adhesive is required, thus leading to a high cost. Namely, such a fuel hose requires an outer layer, an adhesive layer and an inner layer at the minimum and will be a multilayer hose of at least three layers. Generally, as the number of layers increases, the number of extruders to be used increases, thus leading to a high cost.
Further, a fuel hose is basically subjected to bending at various angles over the entire length of a straight tube produced by extrusion molding, in order to adapt it to configurational or spacial restrictions in a specific structure of each automobile. The bending of the hose not only increases a process step, but wrinkles may thereby be formed. Once wrinkles are formed, the stress will be concentrated at such a portion, whereby there will be a problem that the useful life of the hose tends to be substantially short.
It is an object of the present invention to provide a fuel hose which has a double layer structure excellent in interlaminar adhesion without using an adhesive and comprising an inner layer made of a fluororesin having an antistatic function and an outer layer adjacent thereto, and which can be mounted on an automobile, preferably without bending.